1. Field of the Invention
The present invention is generally related to vehicle collision detecting methods by which a collision safety device (such as, an air bag system and a belt retracting system) is properly started.
2. Description of the Related Art
In an air bag system for protecting an occupant from a secondary collision damage upon collision of a vehicle, if only an acceleration signal which an acceleration sensor outputs as a starting or triggering signal for the air bag system is used, there is a possibility that a starting signal may be outputted when a small object which will not substantially damage a vehicle body collides against a portion of the vehicle near where the acceleration sensor is located. Therefore, means for preventing this is required.
Further, the air bag system is required to be operated not only when a collision with a large shock occurs, but also when a collision with a small but continuously long shock occurs. In such a case, however, there is a possibility that the starting signal may not be produced by the acceleration sensor and hence, means for compensating for this is required.
In order to avoid the above-discussed problems, a collision detecting method has been proposed having the step of calculating a speed found by integration of an acceleration produced by an acceleration sensor (i.e., a secondary collision speed at which an occupant moves, for example, toward a steering wheel under an action of an inertia due to a collision) so that if the secondary collision speed exceeds a predetermined value, a starting signal for an air bag system is produced (see, Japanese Patent Publication No. 8574/84).
In the above-described conventional method, however, when a collision with a small and continuously long shock occurs, a fairly long time may lapse from an instant of collision until the starting signal for the air bag system is produced; thereby, resulting in a possibility of some deviation in the timing for the start of the air bag system.